Embedded wafer level ball grid array (eWLB) is a packaging technology for integrated circuits (ICs) where package interconnects are applied on an artificial wafer or carrier made of individual semiconductor dies (chips) and a molding compound. The semiconductor dies are embedded (overmolded) in the molding compound. A redistribution layer is applied to a side of the eWLB wafer at which the pads of the dies are available. Electrical connections are formed between the die pads and the redistribution layer. Solder bumps are provided on the redistribution layer to enable package mounting after sawing of the eWLB wafer into individual IC packages.
Many types of semiconductor dies require contact at the front and back sides of the die e.g. to provide heat dissipation and/or electrical connectivity (in the case of vertical devices). Conventionally, backside metallization is applied to dies embedded in an eWLB-type package after molding of the dies. The backside metallization processing is done using the final artificial wafer thickness, which can result in warpage issues. For backside heat sinks, another conventional approach is to use a different package technology for connecting the heat sink to the backside of the embedded dies which adds to the overall cost. For other types of semiconductor dies such as acoustic or pressure sensors, light emitters and light sensors, etc., a material is provided at the backside of the dies to provide the necessary coupling (acoustic coupling, optical coupling, pressure coupling, etc.). Conventional approaches for these types of embedded dies involve applying the backside material after the die molding process or by using an additional package technology, again resulting in warpage issues and/or higher unit package cost.